I feel like there's a tangible difference between the 2 themes. At its core, Night Terrors is about the terrifying madness of sleep deprivation, the slow descent into loosing control of your mind & grip on reality... and the episode does a marvelous job at putting us in there with them
Schisms is about the Bogeyman who comes in your sleep to do unthinkable things while you are vulnerable, leaving behind the trace of subconscious trauma. It really reaches its peak creep factor in the holodeck recreation.
Granted, both episodes are great Halloween fare, & my favorite depends on how you rate them. Schisms is a better overall execution, but if you're like me & just love to watch the actors do their thing, then Night Terrors is a better choice because you can revel in watching all the cast members totally nail every moment of mental decay, & it sustains the creep factor throughout multiple scenes.
I've never felt more hopelessness from that show than Picard confiding their dire circumstances to Data, who he knows may be their only hope, & the utter dejection he exudes at seeing Data fail to display an adequate level of emotional investment.
Data has "iced" a number of people over the course of the show, his last moments with Kila Marr & Kivas Fajo for example, but that one with Picard really hurt lol